1. Field of the Invention
This invention relates to vacuum interrupters and, more particularly, to vacuum interrupters whose vacuum enclosures utilize polymeric systems, such as a cured epoxide resin, for sealing and may additionally utilize such systems for one or more other parts of the vacuum enclosures.
2. Description of the Prior Art
Conventional vacuum interrupters are constructed of enclosures of ceramic or glass insulators, which are metallized and brazed to support metallic members, such as of stainless steel or copper-nickel alloys, in turn joined to copper contact rods. A metal bellows on one end of the enclosure allows motion of one contact brazed to one of the contact rods. Within the insulators a protective shield may be provided to prevent thermal shock and metallic contamination from depositing onto the insulators as a result of arc erosion of the contacts during the operation of the interrupter.
Vacuum interrupters have high production costs due to the expensive, high quality materials and processing required which have limited their application to medium and low voltage switching apparatus and large motor contactors. Following assembly and then simultaneous evacuation and braze sealing in vacuum furnaces, the internal pressure in the vacuum interrupter is typically less than about 10.sup.-6 Torr. In service, the internal pressure in a medium voltage interrupter for switchgear may not generally exceed about 2.times.10.sup.-3 Torr. Vacuum interrupters for 600 volt class contactors may not exceed internal pressures on the order of 10.sup.-1 to 10.sup.-2 Torr. Such vacuums must be maintained over a service life of many years.
A conventional vacuum interrupter requires a number of expensive parts and processing steps to achieve a high quality, long endurance vacuum enclosure. These include:
(1) gastight ceramic tubes (typically alumina) which are dimensionally stable and expensive to produce to the required close tolerances, and which must be capable of several excursions to high temperatures (typically up to about 1550.degree. C.) for metallizing and brazing;
(2) the ends of the ceramics must be coated with metal bearing slurries and subsequently fired in a controlled composition atmosphere furnace to provide a metallized surface to which brazing alloys will adhere for impervious and strong joints; and
(3) stainless steel bellows which are subject to multiple excursions to temperatures up to about 1000.degree. C. for brazing.
It is desirable to provide quality vacuum interrupters with lower cost materials and lower temperature processing with fewer heating cycles.